1. Field of the Invention
This invention relates to a dual braking device for a power winch, particularly to one able to quickly stop both the rotating shaft of a motor and the spindle driven by the rotating shaft when the power winch is electrically disconnected to avoid wear of the spindle and the transmitted components, able to surely brake the whole power winch and lower the probability of accidents.
2. Description of the Prior Art
A power winch, also called as a hoisting winder, is a hoisting apparatus able to retract or release steel ropes for slinging up or lowering down heavy loads. A power winch can be positioned on a high building for slinging or lowering goods, or assembled on a jeep or on a cross-country vehicle for trailing other vehicles or for rescuing people in danger. A power winch has to be provided with a braking device so that when circuit is broken (whether by pressing a stop button or due to abrupt power outage), the power winch can be timely stopped operating. A conventional braking device for a power winch, as disclosed in a U.S. Pat. No. 6,520,486, titled “BRAKING DEVICE FOR MOTIVE WINCH”, which was a patent of the inventor of the present invention, as shown in FIG. 1, includes a reduction device 1 composed of a sectional shaft 11, an elastic member 12, a first engraved block 13, a second engraved block 14 and a clutch base 15. The first engraved block 13 is fitted on the sectional shaft 11 and secured thereon with a braking lining 131 able to contact with or separate from a frictional surface 16 formed in the reduction device 1 for performing braking or not. The elastic member 12 is assembled on the first engraved block 13, able to produce a proper reverse torsional force relative to the first engraved block 13 and force the braking lining 131 of the first engraved block 13 to be ready to push against the frictional surface 16 of the reduction device 1. The second engraved block 14 is combined with the sectional shaft 11 for rotating together synchronously. The first and the second engraved block 13, 14 have their corresponding side edges respectively formed with a slope (13A), (14A), which are able to closely contact with each other for pushing the braking lining 131 on the first engraved block 13 to carry out braking, and also respectively formed with an actuating projection (13B), (14B) to be pushed and rotated by the projecting block fixed on the inner side of the clutch base 15. The clutch base 15 is actuated to rotate by a spindle (S1) driven by the motor. Thus, when the motor is operated, the clutch base 15 will be driven to actuate the two engraved blocks 13, 14 to rotate together to let the braking lining 131 move away from the frictional surface 16 of the reduction device 1 to stop braking. When the motor stops operating, the reaction torsional force coming from the heavy loads hung on the steep rope will force the slope (14A) of the second engraved block 14 to push the slope (13A) of the first engraved block 13 and actuated the braking lining 131 to move and closely contact with the frictional surface 16 of the reduction device 1, thus achieving effect of braking. The foresaid structure is the main braking device for a conventional power winch.
Although the braking device for a power winch disclosed in the U.S. Pat. No. 6,520,486 and described above is excellent in use, yet there is still certain respect that has to be improved. As mentioned above, the spindle (S1) is driven by the motor; therefore, when the motor is electrically disconnected, the motor itself, based on inertia action, will rotate the spindle (S1) continuously for a little while. Thus, when the power winch carrying a light load is broken, the gliding distance of braking may become comparatively long, and this situation is likely to cause unexpected accidents. In the braking device for a winch disclosed in the U.S. Pat. No. 6,520,486 mentioned above, although braking is surely done by the reduction device 1, yet the spindle (S1) and the cultch base 15 still may be pushed to rotate by inertia action, thus causing wear to the components and lowering their service life.
To improve the above-mentioned defects, an auxiliary second braking device for a power winch is additionally disposed between the motor and the spindle so that when the motor is electrically disconnected, both the rotating shaft of the motor and the spindle can be timely stopped rotating, able to lower the probability of accidents.